Most dovetail slides use a tapered gib. Why?
When making a dovetail slide, do you have to also machine one of the dovetails with a taper to match the gib? Or is it just that the setscrews on one side of the gib will be turned in a lot more than the other side?
I guess I am wondering why the gib is not just a piece of flat stock with no taper.
Thanks for any insight.
Rick
----- Original Message ----- From: "rick" Newsgroups: rec.crafts.metalworking Sent: Monday, September 27, 2004 6:39 PM Subject: why are gibs tapered?
So the clearance can be adjusted with only a single pair of screws, while also allowing lube oil to flow from center--the middle of these are scraped away so that only the ends are making positive contact....once the center area is hollowed away, only one of the two ends needs to be scraped in to give a tight accurate fit at both ends while still allowing for adjustability........
One of the doves out of the four are tapered, the screw on the fat end is used to set the clearance, the other screw is just to keep the strip from self-tightening and jamming when the slide travel is reversed.
There *are* some dovetail systems in use having a single flat bar and quite a few takeup setscrews as well as some gib systems in use having flat bar and straps on box way systems.......
Basically, it mostly boils down to later ease of adjustment for wear, provided everything was accurate on initial manufacture and assembly to begin with.
Thanks. I sorta see now. I think I may just try a flat bar gib first and see how it goes. I can find no source of info or book on calculating correct tapers for gibs and dovetails anyway. I don't know if the gingery books/plans cover this?
Rick
Aside from the information provided already, the tapered gib is infinitely stronger then a series of set screws pushing on the gib because the tapered gib "fills" all the available space save some running clearance. No load could compress the gib, while it is conceivable that the point loading on the strait gib / gib screws might be sufficient to crush down somewhat or even cause complete breakdown under heavy cutting conditions akin to interrupted cutting.
Dave uses the flat-bar-with-several-screws method. --Glenn Lyford
With that method, you generally set the two outside screws to produce the desired minimum "drag", then dont mess with them after that........the inner ones serve as locks and to distribute some of the load......
If you over tighten the inner ones, it takes too much pressure from the outer ones, and the slide will exibit side/side rock or slop.
HTH
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